Rod reducing device

ABSTRACT

A rod reducer includes a housing, an anvil, a locking anvil configured to engage a locking plug of a bone screw assembly, an arm assembly, a reducing screw extending through the housing and rotatably coupled with the anvil, and a locking screw extending through the housing and rotatably coupled with the locking anvil. The arm assembly includes an arm hingedly coupled to the housing, and first and second grasping members configured to engage the bone screw assembly. The first and second grasping members are hingedly coupled to the housing and extend through the anvil. Rotation of the reducing screw transitions the arm assembly between an open position, in which, distal portions of the arm and the first and second grasping members are radially expanded, and a closed position, in which, the distal portions of the arm and the first and second grasping members are radially contracted.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of U.S. Provisional Application Ser. No. 62/447,519, which was filed on Jan. 18, 2017, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to spinal surgery and, more particularly, to systems, devices, and methods for reducing spinal rods into bone screw housings and/or for manipulation of a spinal column.

BACKGROUND

There are various disorders, diseases and types of injury, which the spinal column may experience in a lifetime. One of the more common solutions to treating these conditions involves a surgical procedure utilizing mechanical hardware. The mechanical hardware used to immobilize the spinal column typically involves a series of bone screws and spinal rods or plates. When the spine surgery is performed, it is common practice to place bone screws into the vertebral bodies and then connect a spinal rod between adjacent vertebral bodies.

The process of properly inserting the spinal rod into the receiving slot of a bone screw and then securing that connecting spinal rod in place often can require that the surgeon use a number of instruments and expend a great deal of time and effort to accomplish the task. When bone screws in several adjacent vertebrae are to be securely connected by a spinal rod, the repeated process of inserting the spinal rod into the heads of the bone screws and then securing the spinal rod in place for each respective bone screw can be difficult, tiresome and time consuming. Further, the alignment of the spinal rod as it connects to each of the sequential bone screws may require adjustment during the procedure and, therefore it is beneficial that a device and method be provided by which the spinal rod can be reduced into the head of each of the sequentially aligned bone screws and, as desired, easily adjusted so as to facilitate the process for the surgeon with minimal effort and loss of time.

For these reasons there remains a need for a device that is capable of securely grasping the head of a bone screw in a controlled, measured manner and reducing a spinal rod into the head of that bone screw in such a way as to permit easy position adjustment as other portions of the spinal rod are reduced into other bone screws.

SUMMARY

In accordance with an embodiment of the present disclosure, there is provided a rod reducer that effectively reduces in a controlled, measured way a spinal rod into position in a head of a bone screw and holds that spinal rod in position while other portions of the spinal rod are positioned and reduced into other bone screws allowing for position adjustment as necessary during the process. The rod reducer includes a housing, an anvil, a locking anvil, an arm assembly, a reducing screw, and a locking screw. The anvil is operatively coupled with the housing, and includes a rod positioning portion configured to engage a spinal rod. The locking anvil is configured to engage a locking plug of a bone screw assembly. The arm assembly includes an arm hingedly coupled to the housing and extending through the anvil, and first and second grasping members configured to engage the bone screw assembly. The first and second grasping members are hingedly coupled to the housing and extend through the anvil. The reducing screw extends through the housing and is rotatably coupled with the anvil. The locking screw extends through the housing and is rotatably coupled with the locking anvil. Rotation of the reducing screw transitions the arm assembly between an open position, in which, distal portions of the arm and the first and second grasping members are radially expanded, and a closed position, in which, the distal portions of the arm and the first and second grasping members are radially contracted.

In an embodiment, the reducing screw may be rotatably coupled with the anvil while inhibiting relative axial displacement therebetween.

In another embodiment, the housing may define a plurality of cutouts dimensioned to receive the arm and the first and second grasping members.

In yet another embodiment, the anvil may include an elongate member defining a threaded bore configured to threadably engage the locking screw.

In still yet another embodiment, the locking screw may be rotatably coupled with the locking anvil while inhibiting relative axial displacement therebetween.

In another embodiment, the first and second grasping members may define first and second guide channels dimensioned to engage the bone screw assembly when the arm assembly is in the closed position.

In yet another embodiment, the rod positioning portion of the anvil may define an arcuate recess configured to engage the spinal rod.

In still yet another embodiment, the reducing screw may threadably engage the housing.

In an embodiment, the anvil may define a cutout configured to slidably receive at least a portion of the locking anvil to facilitate axial displacement of the locking anvil relative to the anvil.

In accordance with another embodiment of the present disclosure, there is provided a system for reducing a spinal rod into a bone screw assembly including a spinal rod, a bone screw assembly, and a rod reducer. The bone screw assembly includes a rod receiving portion configured to receive the spinal rod, and a housing including a locking plug transitionable between a locked state, in which, the spinal rod is securely fixed to the rod receiving portion and an unlocked state, in which, the spinal rod is repositionable with respect to the rod receiving portion. The rod reducer includes a housing, an anvil operatively coupled with the housing, a locking anvil configured to engage the locking plug of the bone screw assembly, an arm assembly, a reducing screw, and a locking screw. The anvil includes a rod positioning portion configured to engage the spinal rod. The arm assembly includes an arm hingedly coupled to the housing and extending through the anvil, and a pair of grasping members configured to engage the bone screw assembly. The pair of grasping members is hingedly coupled to the housing and extends through the anvil. The reducing screw extends through the housing and is rotatably coupled with the anvil. The locking screw extends through the housing and is rotatably coupled with the locking anvil. Rotation of the reducing screw transitions the arm assembly between an open position, in which, distal portions of the arm and the pair of grasping members are radially expanded, and a closed position, in which, the distal portions of the arm and the pair of grasping members are radially contracted.

In an embodiment, rotation of the locking screw may cause axial displacement of the locking anvil relative to the anvil.

In another embodiment, the arm may be configured to engage the rod receiving portion of the bone screw when the arm assembly is in the closed position.

In yet another embodiment, the locking anvil may be configured to impart axial force to the locking plug of the bone screw assembly to transition the housing of the bone screw assembly between the unlocked state to the locked state.

In accordance with another aspect of the present disclosure, there is provided a method of reducing a spinal rod including transitioning a rod reducer to an open state, in which, distal ends of an arm and grasping members of the rod reducer are radially expanded; mounting the rod reducer over a bone screw assembly; positioning a spinal rod adjacent a rod receiving portion of the bone screw assembly; rotating a reducing screw of the rod reducer to transition an anvil of the rod reducer away from a housing of the rod reducer to a closed state, in which, the distal ends of the arm and the grasping members of the rod reducers are radially contracted to engage the bone screw assembly; reducing the spinal rod into the rod receiving portion; and securing the spinal rod to the rod receiving portion by rotating a locking screw of the rod reducer to advance a locking plug into a bone screw housing of the bone screw assembly.

In an embodiment, rotating the reducing screw of the rod reducer may include engaging the arm of the rod reducer with the rod receiving portion of the bone screw.

In another embodiment, rotating the reducing screw of the rod reducer may include engaging the grasping members with the bone screw housing of the bone screw assembly.

In yet another embodiment, partially inserting the locking plug into the bone screw housing of the bone screw assembly may include making adjustments to the spinal rod.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and, together with a general description of the disclosure given above, and the detailed description of the embodiment(s) given below, serve to explain the principles of the disclosure, wherein:

FIG. 1 is a front view of a rod reducer and a bone screw assembly in accordance with an embodiment of the present disclosure;

FIG. 2 is a perspective view of the rod reducer of FIG. 1;

FIG. 3 is a side view of the rod reducer of FIG. 2;

FIG. 4 is an exploded perspective view of the rod reducer of FIG. 1 with parts separated;

FIG. 5 is a perspective view of a housing of the rod reducer of FIG. 1;

FIG. 6 is a perspective view of an anvil of the rod reducer of FIG. 1;

FIG. 7 is a top view of the rod reducer of FIG. 2;

FIG. 8 is a cross-sectional view of the rod reducer of FIG. 7 cut along a section line 8-8;

FIG. 9 is a front view of the rod reducer of FIG. 1 illustrating the reducing device in an open position;

FIG. 10 is a side view of the rod reducer and the bone screw assembly of FIG. 1 illustrating the rod reducer mounted on the bone screw assembly;

FIG. 11 is a front view of the rod reducer and the bone screw assembly of FIG. 1 illustrating the rod reducer mounted on the bone screw assembly;

FIG. 12 is a side view of the rod reducer and the bone screw assembly of FIG. 1 illustrating use with a spinal rod;

FIG. 13 is a front view of the rod reducer and the bone screw assembly of FIG. 12 illustrating reduction of the spinal rod;

FIG. 14 is a rear view of the rod reducer and the bone screw assembly of FIG. 13; and

FIG. 15 is a rear view of the rod reducer and the bone screw assembly of FIG. 14 illustrating a locking anvil engaging a locking plug of the bone screw assembly.

DETAILED DESCRIPTION

Embodiments of the presently disclosed devices are described in detail with reference to the drawings, in which like reference numerals designate identical or corresponding elements in each of the several views. As used herein, the term “distal” or “leading” refers to that portion of the device that is farther from the user, while the term “proximal” or “trailing” refers to that portion of the device that is closer to the user. In addition, the term “cephalad” is known to indicate a direction toward a patient's head, whereas the term “caudad” indicates a direction toward the patient's feet. Further still, the term “lateral” is understood to indicate a direction toward a side of the body of the patient, i.e., away from the middle of the body of the patient. The term “posterior” indicates a direction toward the patient's back, and the term “anterior” indicates a direction toward the patient's front. As used herein, the term “clinician” refers to a doctor, nurse, or other care provider and may include support personnel. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail.

With reference to FIGS. 1-3, a system for reducing a spinal rod is shown and generally designated as 10. The system 10 for reducing a spinal rod 300 (FIG. 14) includes a rod reducer 100, a bone screw assembly 200, and the spinal rod 300. The rod reducer 100 is configured to be mounted on the bone screw assembly 200 to reduce the spinal rod 300 into a bone screw housing 207 of the bone screw assembly 200. The rod reducer 100 includes a housing 116, an anvil 118 configured to engage the spinal rod 300 to place the spinal rod 300 in the bone screw housing 207, an arm assembly 120 operatively coupled with the housing 116, a locking anvil 130 (FIG. 4) configured to engage a locking plug 209 of the bone screw assembly 200 in order to securely fix the spinal rod 300 with the bone screw assembly 200, a reducing screw 112 operatively coupled with the anvil 118, and a locking screw 114 operatively coupled with the locking anvil 130 (FIG. 4). The housing 116 and the anvil 118 may be unitary structures.

With reference to FIGS. 4 and 5, the housing 116 includes a body 116 a defining a bore 140 configured to threadably receive the reducing screw 112 therein, and a recess 138 dimensioned to receive the locking screw 114 therein. The housing 116 includes cutout portions 158 a, 158 b, 158 c. The cutout portion 158 a defines opposing holes 119 a dimensioned to receive a pin 120 a to hingedly secure an arm 126 of the arm assembly 120 (FIG. 1) to the housing 116. Similarly, the cutout portions 158 b, 158 c define respective holes 119 b, 119 c dimensioned to receive respective pins 120 b, 120 c to hingedly secure respective grasping members 128 a, 128 b of the arm assembly 120 to the housing 116. The cutout portions 158 b, 158 c may oppose each other such that the grasping members 128 a, 128 b may engage diametrically opposed portions of the bone screw housing 207 (FIG. 1) of the bone screw assembly 200 for secure and balanced engagement with the bone screw assembly 200. The bore 140 may be centrally defined in the body 116 a, and the recess 138 may be interposed between the cutout portions 158 b, 158 c. In addition, the recess 138 may include an arcuate profile to receive the locking screw 114.

With particular reference to FIG. 4, the reducing screw 112 includes a distal portion 112 a defining an annular groove 154 a configured to rotatably engage a tongue portion 148 a (FIG. 6) of a third hole 140 b defined in a base portion 118 a of the anvil 118, a proximal portion 112 b defining a cavity 132 a, and a threaded portion 112 c extending between the proximal and distal portions 112 a, 112 b. The cavity 132 a includes, e.g., a hex, key feature for non-slip engagement with a driver or other instrument (not shown) to drive the reducing screw 112. Similarly, the locking screw 114 includes a distal portion 114 a defining an annular groove 155 a configured to rotatably engage a tongue portion 149 of the locking anvil 130, a proximal portion 114 b defining a cavity 132 b, and a threaded portion 114 c extending between the proximal and distal portions 114 a, 114 b. The cavity 132 b includes, e.g., a hex, key feature for non-slip engagement with a driver or other instrument (not shown) to drive the locking screw 112. It is contemplated that cavities 132 a, 132 b may have any suitable configuration such as, e.g., slotted, square, star fitting, or a Phillips head, for engagement with the driver. It is also envisioned that the threaded portions 114 c of the locking screw 114 may be, e.g., a coarse acme thread, configured to support more load, whereas the threaded portion 112 c on the reducing screw 112 may be a finer thread.

With reference now to FIGS. 4 and 6, the anvil 118 includes a base portion 118 a, an elongate portion 145 extending proximally from the base portion 118 a, and a pair of rod positioning portions or rod positioning members 146 (only one shown) extending distally from the base portion 118 a. The base portion 118 a defines a hole 134 dimensioned to receive the arm 126 therethrough, second holes 136 a, 136 b dimensioned to receive the respective grasping members 128 a, 128 b therethrough, and a third hole 140 b dimensioned to receive the reducing screw 112. In particular, an inner wall 148 of the third hole 140 b includes a tongue portion 148 a extending radially inward from the inner wall 148. The tongue portion 148 a is configured to engage the annular groove 154 a of the reducing screw 112 such that the reducing screw 112 is rotatably secured with the anvil 118, while inhibiting relative axial movement with the anvil 118. The elongate portion 145 extends proximally from the base portion 118 a. The elongate portion 145 defines a threaded bore 145 a configured to threadably engage the locking screw 114. The rod positioning members 146 extend distally from the base portion 118 a and are configured to engage the spinal rod 300 (FIG. 14) to position the spinal rod 300 into the bone screw housing 207 (FIG. 1) of the bone screw assembly 200.

The base portion 118 a further defines a locking pin hole 123 (FIG. 4) dimensioned to receive a locking pin 122. The locking pin 122 is configured to limit axial displacement of the locking screw 114. The base portion 118 a can further define a cam pin hole 125 that extends across a portion of the hole 134. The cam pin hole 125 can be configured and dimensioned to receive a cam pin 124 (FIG. 4). Under such a configuration, when the rod reducer 100 transitions between open (FIG. 9) and closed positions (FIG. 2), i.e., radial expansion and contraction of the arm 126 and the grasping members 128 a, 128 b, camming portions 160 a, 160 b of the arm 126 can slidably engage the cam pin 124. In the open position (FIG. 9), each of the arm 126 and the grasping members 128 a, 128 b defines an acute angle with respect to a central longitudinal axis of the housing 116. In the closed position (FIG. 2), each of the arm 126 and the grasping members 128 a, 128 b is substantially parallel with the central longitudinal axis of the housing 116.

With reference to FIGS. 4 and 8, the arm assembly 120 includes the arm 126 and first and second grasping members 128 a, 128 b configured to engage the bone screw housing 207 (FIG. 14). The arm 126 is dimensioned to extend through the first hole 134 (FIG. 6) of the anvil 118. The arm 126 includes a distal portion 126 a and a proximal portion 126 b. The proximal portion 126 a is hingedly coupled to the cutout portion 158 a (FIG. 5) of the housing 116 by the pin 120 a. The proximal portion 126 b includes the camming portion 160 a, and the distal portion 126 a includes a camming portion 160 b having a longitudinally tapered surface. Such a configuration facilitates transition of the arm 126 between the radially contracted (closed) and radially expanded (open) positions. Each of the elongate grasping members 128 a, 128 b may also include respective camming portions 161 a, 161 b in order to facilitate radial contraction and expansion thereof. Each of the grasping members 128 a, 128 b includes respective lobes 166 a, 166 b. Each lobe 166 a, 166 b defines a guide channel 168 a, 168 b (only 168 b shown) dimensioned to engage the bone screw housing 207 of the bone screw assembly 200.

With continued reference to FIGS. 4 and 8, the locking anvil 130 defines a cavity 131 dimensioned to receive the distal portion 114 a of the locking screw 114. In particular, the locking anvil 130 includes a tongue portion 149 received in the annular groove 155 a of the locking screw 114 to rotatably secure the locking anvil 130 with the locking screw 114, while inhibiting relative axial movement therebetween. Under such a configuration, the locking anvil 130 may be moved relative to the anvil 118. The locking anvil 130 includes a guide 130 c dimensioned to be slidably received in a cutout 118 c defined in the anvil 118 in order to guide axial movement of the locking anvil 130. Under such a configuration, the clinician may rotate the locking screw 114 in order to move the locking anvil 130 toward and away from the anvil 118.

With reference now to FIG. 10, the bone screw assembly 200 includes the bone screw housing 207 configured to receive a locking plug 209 (FIG. 14), a threaded shaft 205 extending distally from the bone screw housing 207, and a rod receiving portion 203 disposed adjacent the bone screw housing 207. With brief reference to FIG. 14, when the locking anvil 130 engages the locking plug 209, through rotation of the locking screw 114, the locking plug 209 is advanced into the bone screw housing 207, which, in turn, causes the rod receiving portion 203 to grasp the spinal rod 300 disposed therein, thereby securing the spinal rod 300 with the bone screw assembly 200. The locking plug 209 is movable amongst an open or unlocked state that allows insertion and/or removal of the spinal rod 300, a partially locked state that allows rotation and longitudinal movement of the spinal rod 300 relative to the bone screw assembly 200, and a locked state that securely fixes a position of the spinal rod 300 with respect to the bone screw assembly 200. This arrangement allows the clinician to reduce the spinal rod 300 into the rod receiving member 203 while still being able to perform additional adjustments to the spinal rod 300 during the procedure.

In use, initially, the bone screw assembly 200 is mounted to a vertebra (e.g., screwed in to the vertebra) of a spine (not shown) such that the rod reducer 100 can be mounted on the bone screw assembly 200. With reference to FIG. 9, the rod reducer 100 is initially placed in an open position, in which, the arm 126 and the grasping members 128 a, 128 b are radially expanded by placing the reducing screw 112 in, e.g., a proximal-most position, in which the anvil 118 is positioned adjacent the housing 116. Under such a configuration, the distal portion 126 a of the arm 126 and the lobes 166 a, 166 b of the grasping members 128 a, 128 b are spaced apart to receive the bone screw housing 207. In order to mount the rod reducer 100 to the bone screw assembly 200, the rod reducer 100 is positioned over the proximal portion of the bone screw assembly 200 (FIG. 1).

The arm 126 and the grasping members 128 a, 128 b are hingedly coupled to the housing 116 such that the arm 126 and the grasping members 128 a, 128 b can rotate radially outward about the respective pins 120 a, 120 b, 120 c (FIG. 4) and transition between the radially contracted (closed) (FIG. 2) and expanded (open) (FIG. 9) positions. As the anvil 118 moves away from the housing 116, the cam pin 124 (FIG. 8) slides against the camming portion 160 a, 160 b (FIG. 4) of the arm 126. Similarly, as the anvil 118 moves away from the housing 116, the camming portions 161 a, 161 b (FIG. 4) of each of the grasping members 128 a, 128 b slide against the anvil 118. In this manner, the clinician can rotate the reducing screw 112 in order to move the anvil 118 distally, which, in turn, causes the arm 126 and the grasping members 128 a, 128 b to transition to the closed position. At this time, the lobes 166 a, 166 b of the grasping members 128 a, 128 b are secured with the bone screw housing 207, and the distal portion 126 a of the arm 126 engages the rod receiving member 207 of the bone screw assembly 200.

At this time, the spinal rod 300 (FIG. 14) may be placed adjacent the rod receiving member 203 (FIG. 12) of the bone screw assembly 200. Alternatively, the spinal rod 300 may be placed adjacent the rod receiving member 203 prior to mounting the rod reducer 100 to the bone screw assembly 200. The clinician can further rotate the reducing screw 112 to move the rod positioning member 146 of the anvil 118 to reduce the spinal rod 300 into the rod receiving recess 203 of the bone screw assembly 200.

With reference to FIGS. 12 and 14, the spinal rod 300 may be secured in the rod receiving recess 203 of the bone screw assembly 200 by utilizing the locking plug 209. In particular, the locking screw 114 may be rotated causing the locking anvil 130 to move relative to the anvil 118 toward the locking plug 209. With additional reference to FIG. 15, additional displacement of the locking anvil 130 advances the locking plug 209 into the bone screw housing 207, which, in turn, causes the spinal rod 300 to be securely fixed in the rod receiving recess 203. In this manner, the locking anvil 130 contacts the locking plug 209 and causes an interference fit which grips the spinal rod 300. It is also envisioned that the locking plug 209 may be partially locked or advanced into the bone screw housing 207 in order to make further adjustments to the spinal rod 300 as described hereinabove.

Persons skilled in the art will understand that the structures and methods specifically described herein and shown in the accompanying figures are non-limiting exemplary embodiments, and that the description, disclosure, and figures should be construed merely as exemplary of particular embodiments. It is to be understood, therefore, that the present disclosure is not limited to the precise embodiments described, and that various other changes and modifications may be effected by one skilled in the art without departing from the scope or spirit of the disclosure.

Additionally, the elements and features shown or described in connection with certain embodiments may be combined with the elements and features of certain other embodiments without departing from the scope of the present disclosure, and that such modifications and variations are also included within the scope of the present disclosure. Accordingly, the subject matter of the present disclosure is not limited by what has been particularly shown and described. 

What is claimed is:
 1. A rod reducer comprising: a housing; an anvil operatively coupled with the housing, the anvil including a rod positioning portion configured to engage a spinal rod; a locking anvil configured to engage a locking plug of a bone screw assembly; an arm assembly including: an arm hingedly coupled to the housing and extending through the anvil; and first and second grasping members configured to engage the bone screw assembly, the first and second grasping members hingedly coupled to the housing and extending through the anvil; a reducing screw extending through the housing and rotatably coupled with the anvil; and a locking screw extending through the housing and rotatably coupled with the locking anvil, wherein rotation of the reducing screw transitions the arm assembly between an open position, in which, distal portions of the arm and the first and second grasping members are radially expanded, and a closed position, in which, the distal portions of the arm and the first and second grasping members are radially contracted.
 2. The rod reducer according to claim 1, wherein the reducing screw is rotatably coupled with the anvil while inhibiting relative axial displacement therebetween.
 3. The rod reducer according to claim 2, wherein the housing defines a plurality of cutouts dimensioned to receive the arm and first and second grasping members.
 4. The rod reducer according to claim 1, wherein the anvil includes an elongate member defining a threaded bore configured to threadably engage the locking screw.
 5. The rod reducer according to claim 4, wherein the locking screw is rotatably coupled with the locking anvil while inhibiting relative axial displacement therebetween.
 6. The rod reducer according to claim 1, wherein the first and second grasping members define first and second guide channels dimensioned to engage the bone screw assembly when the arm assembly is in the closed position.
 7. The rod reducer according to claim 1, wherein the rod positioning portion of the anvil defines an arcuate recess configured to engage the spinal rod.
 8. The rod reducer according to claim 1, wherein the reducing screw threadably engages the housing.
 9. The rod reducer according to claim 1, wherein the anvil defines a cutout configured to slidably receive at least a portion of the locking anvil to facilitate axial displacement of the locking anvil relative to the anvil.
 10. A system for reducing a spinal rod into a bone screw assembly comprising: a spinal rod; a bone screw assembly including: a rod receiving portion configured to receive the spinal rod; a housing including a locking plug transitionable between a locked state, in which, the spinal rod is securely fixed to the rod receiving portion and an unlocked state, in which, the spinal rod is repositionable in the rod receiving portion; and a rod reducer including: a housing; an anvil operatively coupled with the housing, the anvil including a rod positioning member configured to engage the spinal rod; a locking anvil configured to engage the locking plug of the bone screw assembly; an arm assembly including: an arm hingedly coupled to the housing and extending through the anvil; and a pair of grasping members configured to engage the bone screw assembly, the pair of grasping members hingedly coupled to the housing and extending through the anvil; a reducing screw extending through the housing and rotatably coupled with the anvil; and a locking screw extending through the housing and rotatably coupled with the locking anvil, wherein rotation of the reducing screw transitions the arm assembly between an open position, in which, distal portions of the arm and the pair of grasping members are radially expanded, and a closed position, in which, the distal portions of the arm and the pair of grasping members are radially contracted.
 11. The system according to claim 10, wherein rotation of the locking screw causes axial displacement of the locking anvil relative to the anvil.
 12. The system according to claim 11, wherein the arm is configured to engage the rod receiving portion of the bone screw when the arm assembly is in the closed position.
 13. The system according to claim 11, wherein the locking anvil is configured to impart axial force to the locking plug of the bone screw assembly to transition the housing of the bone screw assembly between the unlocked state to the locked state. 